Method of making magnetic toroids



y 1960 R. w. SPENCER 2,945,289

- METHOD OF MAKING MAGNETIC TOROIDS Filed June 21, 1954 INVENTOR RICHARDw SPENCER ATTORNEY United States Patent )fl 2,945,289 Patented July 19,1960 ice 2,945,289 METHOD OF MAKING MAGNETIC TOROIDS Richard W. Spencer,Philadelphia, Pa., assignor to Sperry Rand Corporation, a corporation ofDelaware Filed June 21, 1954, Ser. N0. 438,103 '14 Claims. (Cl.29-45557) The present invention relates to novel core structures for usein magnetic devices and is more particularly concerned with a method ofmanufacturing small volume toroids of novel configuration for use insuch devices.

It should be noted before proceeding with the present discussion thatthe method or techniques hereinafter described, as well as the coreconfiguration to be discussed, may be employed in the manufacture ofmagnetic cores of any size. These techniques find particular utility,however, in the provision and fabrication of small-volume magnetictoroidal cores. As is well known, it is often desired that the magneticcore to be used in a device such as a magnetic amplifier, a pulsetransformer, a magnetic memory circuit, or in various other magneticsystems, be of very small size. In the past, this size-limitation hasproduced a considerable problem in core fabrication, inasmuch as, whensmall volumes of magnetic material are being used, the core materialsare most difiicult to work with. In addition, inasmuch as the smallvolumes of magnetic materials which are often desired for use inmagnetic devices of the types mentioned before, have relatively littleinherent strength, it is usually necessary that the said small volumesof magnetic materials be combined with a non-magnetic supportingstructure of greater structural strength, and again the requirement thatsuch a supporting structure be supplied in an extremely small deviceaugments the problems of fabrication. It has accordingly been foundthat, as a matter of practice, when prior art techniques are employed inthe fabrication of small volume magnetic cores, it is most difiicult inlarge quantity by anything resembling a mass production technique, andbecause of this factor the cost of such cores and of the magneticdevices employing such cores is relatively high.

It is accordingly an object of the present invention to provide a methodfor manufacturing magnetic cores, which method permits greater ease inworking with the several core constituents.

Still another object of the present invention resides in providing amethod of working with magnetic materials, in the manufacture ofmagnetic cores, in such a way that the magnetic core material receivesstructural support from a core supporting structure during the actualfabrication of the combined core.

A still further object of the present invention resides in the provisionof a method for manufacturing small volume magnetic toroids, whichmethod permits for mass pr oduction of such toroids and for decreasedcost of individual toroids.

In providing the foregoing objects and advantages of the presentinvention, I employ a method of fabricating a novel magnetic toroidwhich comprises the steps of starting with a relatively thick tube ofmagnetic material, inserting and fastening into the said tube a furthertube of non-magnetic material to provide support for the mag neticmaterial, grinding or otherwise reducing the thickness of the magnetictube so mounted, and slicing the magnetic material.

2 composite structure into individual toroids of desired crossdimension.

The foregoing objects, invention will become following descriptionwhich:

Figure 1 is a perspective view of a magnetic tube and nonmagneticsupport assembled in accordance with the preliminary steps of thepresent invention.

Figure 2 is a representation of a composite magnetic core structureeffected by the method of the present invention, and

Figure 3 depicts a modification of the present invention wherein aplurality of magnetic tubes or toroids are employed in place of thesingle tube shown in Figure 1.

Referring now to the several figures shown, it will be seen that I firstprovide a tube of magnetic material 10, which tube 10 has a thickness 11substantially larger than that desired in the final magnetic toroid. Thetube It) may be fabricated of any material exhibiting desired magneticproperties, such as sintered ferrites, or of other magnetic materialssuch as 5050 Nickel Iron (Deltamax, Orthonik, etc.) or 4-79Moly-Permalloy. These latter magnetic materials may exhibit flux-currentcurves which are substantially rectangular in configuration andtherefore may be employed when such a flux-current curve is desired ofthe final magnetic toroid. Into the central opening of the tube 10 Iinsert a further tube 12 of a non-magnetic material. The tube 12 isselected to have a thickness 13 such as to exhibit a structural strengthconsonant with the requirements of the final structure, and the diameterof the tube 12 is so chosen that the non-magnetic tube 12 fits closelyinto the tube 10 of The tube 12 is then preferably cemented in placewithin the magnetic tube 10 to effect a composite structure as shown inFigure 1.

Non-magnetic tube 12 may be made of a variety of materials, for instanceof an insulating material such as a ceramic or an appropriate fibrousmaterial. The tube 12 may further be fabricated of a non-magnetic metalsuch as l8-8 stainless steel, type 304; Inconel; B-Monel; K-Monel;R-Monel; 315 stainless steel; Nichrome; or metallic titanium. When themagnetic material used for tube 10 comprises a ferrite, it has also beenfound that the supporting tube 12 may be fabricated of brass or of otherrelatively low melting point metals and alloys. When a non-magneticmetal supporting structure is employed for tube 12, the cement utilizedin cementing the tube in place may preferably be of an electricalinsulating nature, or a layer of insulation may preferably be interposedbetween the external peripheral surface of non-magnetic tube 12 and theinternal surface of the magnetic tube 10. It has been found that thisrequirement of insulation is not mandatory, however, and thus, for manymagnetic applications utilizing the magnetic materials enumerated above,no insulation need in fact be provided. This is especially the case whenthe magnetic material comprising tube 10 is a ferrite, and under suchcircumstances the requirement of insulation between the magnetic tubeand the supporting structure may, if desired, be dispensed with. Itshould further be noted that if the tube 12 is in fact chosen of anon-magnetic metal, the actual method of fabricating the compositestructure shown in Figure 1 may be varied so that the tube 1 2 and themagnetic tube 10 mounted thereon are annealed simultaneously, eitherbefore or after the reduction and slicing steps to be described.

Once the insulating or non-magnetic tube 12 is in serted into themagnetic tube 10 and cemented in place as shown in Figure 1, thecomposite structure is mounted and rotated between centers,v forinstance on a lathe, and the external peripheral surface of the saidtube 10 advantages, and practice of my more readily apparent from theand accompanying drawings, in

is then preferably ground to reduce the thickness 11 to i that desiredin the final magnetic toroid. Other methods may of course be employed inthe reduction of the thickness 11, such as other known machiningtechniques, or reduction by chemical action. When the magnetic tube isreduced to the thickness of magnetic material desired in the finalmagnetic core, the composite structure shown in Figure 1 is then slicedin directions substantially perpendicular to the major axis of thecomposite structure, for instance along lines 14, 15, 16 and 17. Thisslicing step may be effected by appropriate saw means such as a diamondsaw having a high peripheral speed.

Referring now to Figure 2, it will be seen that the steps describedpreviously effect a composite magnetic toroid exhibiting an externalannular layer of magnetic material 18 which is supported on, and whichis in close proximity to, an internal tube 19 of non-magnetic or of aninsulating material. The structure shown in Figure 2 defines a centralopening 20, inasmuch as the support 12 was tubular in configuration, andtherefore one or more coils 21 may be wound on the structure in adirection substantially transverse to that of magnetic layer 18.Inasmuch as the winding or windings 21 are in fact disposed as shown, itis preferable to buff or otherwise round the edges of the compositestructure such as 22 and 23 to remove any burrs or other sharpstructures which might be present and which might cause short circuitsbetween the windings 21 and the magnetic'layer 18. In lieu of thispractice, the exterior of the layer 18 and edges 22 and 23 of thecomposite structure may be coated with an insulating material to obviatesuch short circuits, or the windings 21 may be provided with relativelyheavy insulation.

By employing the foregoing techniques, one may produce extremely smallvolume magnetic toroids in relatively large quantity and at relativelysmall cost. The

technique permits the magnetic layer 18 to be reduced to any desiredthickness down to and including a few mils, especially if the spacefactor of the composite core structure is not critical. Further, themethod of the present invention permits the composite structure to bemade to very close tolerances, and inasmuch as the supporting structurefor the final composite core is included within the magnetic materialfrom the very beginning of the fabrication steps, the said supportingstructure, such as tube 12, supports the magnetic material not only inthe final core but also throughout the various steps of grinding, orother reduction of magnetic material thickness, and slicing. Thispermits much greater ease inthe handling of the several materials.

Referring now to Figure 3, it will be seen that in a modification of thepresent invention a plurality of magnetic tubes or toroids 24, 25, 26,etc. may be supported on and cemented to a single supporting tube 27 ofan insulating or non-magnetic material such as has been describedpreviously. The tubes 24, 25, 26, etc. may be of the same or varyingcross dimension and may in fact have a cross dimension such as 28 whichis initially the same as that desired in the final composite corestructure. In this latter case the slicing step would merely slice thesupporting tube 27 between the magnetic tubes or toroids and one neednot slice the magnetic material 24, 25 or 26.

For true mass production techniques, combinations of the structuresshown in Figures 1 and 3 may be employed, and one or more elongatedtubes, such as 10, and/or one or more magnetic toroids such as 24, 25and 26, may be mounted on a single supporting tube 27 whereby theseveral tubular sections of magnetic material may be selectively groundor otherwise reduced to the same or different thicknesses, and thestructure may then be selectively sliced into toroids of the same ordifferent widths.

Variations in the foregoing methods will readily suggest themselves tothose skilled in the art. In particular, the various techniques forreducing the thickness of the magnetic materials may take a number ofdifferent forms and similarly the slicing steps may be effected bydiffering devices. Again, as mentioned previously, the magnetic tube 10may be annealed (or fired, if a ferrite is employed) prior to insertionof the supporting tube 12, or if the said tube 12 is of a non-magneticmetal, or of an insulating material which will not be damaged byannealing temperatures, the structure may be assembled as shown inFigures 1 and/or 3 and the composite structure then can be annealedsimultaneously. (Ferrites, having been fired, would of course require noannealing.) The actual conditions of temperature, pressure, atmosphereand time period of anneal will vary with the various materials employed,and these conditions are well known to those skilled in the art. Itshould be noted that if the composite structure of magnetic tube andsupporting tube are to be annealed simultaneously, the materials shouldbe so chosen that the supporting tube will not adversely aifect themagnetic properties of the magnetic metal during the annealing step. Thematerials discussed previously for the several components of thecomposite structure satisfy this requirement.

Having thus described my invention, I claim:

1. The method of making a substantially toroidal magnetic structurewhich comprises the steps of inserting an elongated tube of non-magneticmaterial having appreciable structural strength into a tube of magneticmaterial whereby the internal surface of said magnetic tube is supportedon the external surface of said nonmagnetic tube attaching said tube ofmagnetic material to said tube of non-magnetic material, reducing theexternal diameter of said tube of magnetic material, while it issupported on said non-magnetic tube, to a final thickness of magneticmaterial normally having little structural strength per se, whereby thecomposite structural strength of said reduced diameter of magnetic tubesupported on said non-magnetic tube is derived substantially entirelyfrom said non-magnetic tube, and thereafter slicing said tube ofnon-magnetic material in a direction substantially transverse to themajor axis thereof.

2. The method of claim 1 in which said reducing step comprises grindingthe external peripheral surface of said tube of magnetic material.

3. The method of claim 1 including the step of winding an electricalconductor around the external surface of said reduced diameter magneticmaterial and the in ternal surface of said non-magnetic material in adirection substantially transverse to said magnetic material, subsequentto said slicing step.

4. The method of claim 1 including the step of coating said toroidalcore slice with an insulating material subsequent to completion of saidslicing step.

5. The method of making a substantially toroidal magnetic structurecomprising the steps of inserting an elongated supporting tube of anon-magnetic metal into the central opening of a tube of magnetic metalhaving an initial external diameter substantially in excess of thatdesired in a final core, rigidly attaching said tube of magnetic metalto said non-magnetic supporting tube, reducing the annular crossdimension of said tube of magnetic metal, while it is supported by saidnon-magnetic tube to a relatively small volume of magnetic materialcarried by and supported on the external surface of said nonmagneticmetal tube, and thereafter slicing said combined magnetic andnon-magnetic metal tubes in a direction substantially transverse to themajor axis thereof.

6. The method of claim 5 including the step of anneal-v ing thecomposite slices of magnetic and non-magnetic metals resulting from saidslicing step.

7. The method of claim 5 including thestep of disposing an insulatingcoating between said tubes of magnetic and non-magnetic metals duringsaid inserting step.

8. The method of making a magnetic structure havsaid composite magnetictube ing a relatively small volume of magnetic material comprising thesteps of inserting an elongated hollow supporting member of non-magneticmetal into the central opening of an elongated hollow magnetic tube,cementing the internal surface of said magnetic tube to the externalsurface of said supporting member by means of an adhesive exhibitingelectrical insulation properties, reducing the external diameter of saidmagnetic tube while it is supported by and cemented to said non-magneticmetal supporting member, and thereafter slicing and non-magnetic metalsupporting member in a direction transverse to the direction ofelongation thereof.

9. The method of making a substantially toroidal magnetic structurecomprising the steps of inserting an elongated non-magnetic tubularsupporting member into the central opening of a hollow ferrite tube,attaching the external surface of said non-magnetic tube to and insupporting relation to the internal surface of said ferrite tube,reducing the external diameter of said ferrite tube while it issupported by said non-magnetic tube to effect a final relatively smalltubular volume of ferrite material supported by the external surface ofsaid non-magnetic tubular member, and thereafter slicing said reducedvolume fern'te tube in a direction transverse to the direction ofelongation of said tubular supporting member.

10. A method for making magnetic core devices comprising the steps ofinserting an elongated non-magnetic hollow supporting structure into atube of magnetic material, rigidly attaching said magnetic tube to saidnonmagnetic structure, slicing the composite core composed of saidmagnetic material and supporting structure in a direction substantiallytransverse to the major axis of said supporting structure to formmagnetic cores, and thereafter threading an electrical conductor throughthe hollow supporting structure on each of said composite cores tothereby form a winding on each of said cores whereby said core devicesmay be coupled to a magnetic system.

11. The method of making a substantially toroidal magnetic core having asubstantially rectangular hysteresis characteristic, which comprises thesteps of inserting an elongated tube of non-magnetic material into thecentral opening of a tube of magnetic material, attaching the internalsurface of said magnetic tube to the external surface of saidnon-magnetic insulating tube by 6 suitable adhesive means, slicing saidattached tubes of magnetic and non-magnetic material in a directionsubstantially transverse to the major axis of said insulating tubethereby to provide a substantially toroidal core slice comprising asmall substantially toroidal volume of magnetic material supported onthe external surface of a substantially toroidal volume of non-magneticmaterial, and annealing said magnetic material so that said magneticmaterial exhibits a rectangular hysteresis characteristic.

12. The method of claim 11 step is performed subsequent to prior to saidslicing step.

13. The method of claim 11 wherein said annealing step is performedprior to the step of inserting said elongated tube of non-magneticmaterial into said tube of magnetic material.

14. The method of making a magnetic structure which comprises the stepsof inserting an elongated supporting tube of non-magnetic material intothe central openings of a plurality of tubes of magnetic material,rigidly attaching said magnetic tubes to said non-magnetic supportingtube in spaced relation, reducing the annular cross dimension of each ofsaid tubes of magnetic material while they are so carried by said tubeof non-magnetic material, said reducing step including the step ofgrinding the external peripheral surfaces of said tubes of magneticmaterial, said grinding step being such that different ones of saidmagnetic tubes are reduced to ditferent annular cross dimensions, andthereafter slicing said supporting tube of non-magnetic material betweensaid reduced dimension spaced tubes of magnetic material in a directionsubstantially transverse to the axes thereof.

wherein said annealing said attaching step but References Cited in thefile of this patent UNITED STATES PATENTS 1,758,719 Smith May 13, 19301,880,805 Christopher Oct. 4, 1932 1,896,762 Whittle Feb. 7, 19332,334,584 Rich Nov. 16, 1943 2,467,868 Sommerville Apr. 19, 19492,477,350 Sommerville July 26, 1949 2,488,961 Camilli Nov. 22, 19492,715,659 Ibuka et a]. Aug. 16, 1955

